Radon Research

There are three groups of radon studies that resulted in our determination that radon does indeed cause lung cancer. Below we will review the following types of studies:

  • Underground Miners
  • Animals
  • Human Research Studies

Occupational Miner Studies

  • Linear dose response relationship was found for all the occupational studies
  • A 1994 NCI pooled analyses of 68,000 miners concluded that about 39% of the lung cancer deaths among smokers and 73% of the lung cancer deaths among never-smokers may have been due to their occupational radon progeny exposure
  • Projecting risks to the residential setting they concluded that radon progeny may be responsible for 10 – 12% of lung cancers in smokers and 28 -31% in never-smokers.

Animal Studies

Why Animal Studies so Important?

  • Animal studies confirm radon carcinogenicity and linear dose relationship. The relationship between the amount of exposure (dose) to a substance and the resulting changes in body function or health (response).  – Agency for Toxic Substances and Disease Registry
  • Health effects observed in animals exposed to radon and radon decay products include lung carcinomas, pulmonary fibrosis, emphysema, and a shortening of life-span (U.S. DOE/Office of Energy Research 1988a).
  • Exposure to ore dust or diesel fumes simultaneously with radon did not increase the incidence of lung tumors above that produced by radon progeny exposures alone (DOE/Office of Energy Research 1988a).
  • The incidence of respiratory tract tumors increased with an increase in cumulative exposure and with a decrease in rate of exposure (NAS 1988).

Overview of Human Research Methods

Overview of Human Research Methods:

  • Residential Studies
  • Ecological vs. Case-Control
    • Ecological: Studying a population rather than an individual.
    • Case-Control: Studying individuals with a disease & comparing against individuals without the disease (control group).

Ecological Studies

  • Show the number of lung cancer deaths for a region compared with substitute measures of exposure for that region.
  • Showed a relationship between exposure to radon and an increased risk of lung cancer.

Flaws in Ecological Model:

  • Ecologic studies do not consider information on individual smoking history.
  • Ecologic studies do not consider information on individual mobility.
  • Both of which are important variables in assessing radon risk  
  • Ecologic studies were discontinued and replaced with the more reliable case-control studies.

Case-Control Studies:

  • Compared individuals with lung cancer (cases) to individuals without lung cancer (controls).
  • Both groups compared for differences in home exposures, (using substitute measures of radon exposure).  A number of these studies found an association between indoor exposure to radon and increased lung cancer risk.
  • Scientists determined that when taken individually, some studies don’t have the statistical power for conclusive reporting
  • For this reason, scientists decided to pool data from international studies as they are completed.
  • Recent Case-Control Studies:
    • Pooled studies from Europe, North America & China
    • Notably: Iowa Radon Lung Cancer Study or IRLCS

Pooled Studies:

  • The North American Residential Radon Pooling Study
    • Combined data from twenty residential studies to confirm the radon risks predicted by extensive occupational mining studies 
    • The studies include:
      • Iowa Radon Lung Cancer Study (Epidemiology March 2005)
      • European Residential Radon Pooling Study (British Medical Journal January 2005)
    • By pooling the residential data, studies showed an increased lung cancer risk consistent with the predicted 12% per 2.7 pCi/L based on a linear model developed by the National Research Council.
    • Notice…threshold level of cancer incidence at 2.7 pCi/L (not 4.0 pCi/L).